The Low Battery Trouble That Came Back a Week Later

Why this matters

A panel sent a low battery trouble, a tech replaced a battery that genuinely failed its load test, and a week later the same panel sent the same trouble. The second tech found a healthy new battery and a transformer plugged into an outlet that a wall switch turned off. Both visits were right about the battery. Only one of them read the signal history far enough back to see the line above the low battery signal, and that line had been sending the answer for a month.

The first call

The dealer's station sends AC loss signals to the account history but does not open a service ticket for them, because a storm can produce hundreds in an hour and nearly all restore on their own. A low battery signal does open a ticket. On Monday, April 14, the queue had one: low system battery, received early Sunday morning, restored Sunday mid-morning.

The tech went out that afternoon. The panel was in the closet of a guest bedroom, a hardwired panel with a 12 V sealed lead-acid standby battery whose date label showed it was five years old, older than the replacement interval the panel maker recommends. Before disconnecting anything he called the central station, placed the account on test and had the operator confirm the window, because removing a standby battery sends a low battery or battery missing signal on most panels. See related: How to Put an Alarm Account on Test and Take It Off.

He load-tested the old battery with a battery tester. It showed a normal resting voltage and then collapsed under load, falling well below the tester's pass line within seconds. That is what an aged battery does: enough surface charge to look fine on a meter and nowhere near its rated capacity when asked to carry the panel. He fitted a new battery of the same voltage and capacity, confirmed the panel's own battery test passed, confirmed the station received the restore under the test window, and took the account off test. See related: How to Replace an Alarm Panel Battery and Load Test It.

The diagnosis was correct. The battery had failed. The ticket closed.

The same signal, seven days later

On Monday, April 21 the queue had the same ticket for the same account: low system battery, Sunday morning. The service manager sent a different tech and attached the full signal history for the previous six weeks instead of the single event.

 ACCOUNT EVENT HISTORY (excerpt)
 301 = AC loss   302 = low system battery
 R = restore of the same event

 DATE    TIME   EVENT
 Mar 15  23:30  301 AC loss
 Mar 16  02:15  301 R AC restored
 Apr 12  23:55  301 AC loss
 Apr 13  03:40  302 low system battery
 Apr 13  08:20  301 R AC restored
 Apr 13  11:05  302 R battery restored
 Apr 14  15:10  302 / 302 R  (battery
                replaced, account on test)
 Apr 19  22:50  301 AC loss
 Apr 20  06:55  302 low system battery
 Apr 20  07:30  301 R AC restored
 Apr 20  10:40  302 R battery restored

Reading what the first tech never saw

Every low battery followed an AC loss on the same night. The panel was not draining its battery while on mains power. It was running on battery because it had no mains power, for hours, and the battery eventually ran low.

The AC losses all began late in the evening, and all on weekends. Saturday nights, March 15, April 12 and April 19. A utility outage does not keep a calendar. Something in the house was turning the panel's power off at bedtime and on again in the morning.

The timing on April 12 explains why the old battery failed when it did. The dealer programs AC loss to report after a 60-minute delay, so the 23:55 report means power went off at about 22:55. The low battery came at 03:40, about 4 hours and 45 minutes later. In March the outage ran from about 22:30 to 02:15, under four hours, and ended before the old battery ran low; that night the guests had switched the lamp back on in the small hours. Each of these nights was a deep discharge, and repeated deep discharges age a lead-acid battery fast; by April it could no longer carry the panel for five hours.

The new battery was fine. On April 19 the power went off at about 21:50 and the low battery came at 06:55, about 9 hours and 5 minutes later. A new battery of the same capacity carried the panel nearly twice as long as the failing one had, and then ran low because no battery of that size is meant to carry a panel through every night it is switched off. See related: How to Size a Standby Battery for an Alarm Panel.

So the first tech's diagnosis was right and incomplete. The battery had failed, and the reason it failed was still in the house.

At the house

The homeowner confirmed the pattern without being asked about the outlet: their adult son and his partner stayed in the guest room some weekends, and the room's lamp was on a wall switch by the door.

The panel's plug-in transformer was in the receptacle just outside the closet door, beside the bed. The tech checked it with a non-contact voltage tester and then the room's wall switch. The top half of that receptacle was switched; the bottom half was always on. The transformer was in the top half. The lamp, which had been moved to the other side of the bed, was plugged into the bottom half. With the switch off, the lamp stayed on and the alarm panel lost its power. Nobody in the house would have connected the two.

He also read the panel's own event log, which showed the same AC losses. Every keypad would have shown the AC trouble on those nights, but the household was asleep.

Moving the transformer

Before moving anything he placed the account on test again; pulling the transformer from one socket and plugging it into another produces AC loss and restore events, and with a ticket already open the office did not want another chasing it.

To the unswitched half. He moved the transformer to the bottom, always-on half of the same receptacle and the lamp to the switched half, so the switch now did what the guests expected it to.

Secured. Plug-in transformers for alarm panels usually have a tab or bracket that takes the receptacle's cover plate screw, so the transformer cannot be knocked or pulled out. This one did; the original installer had not used it. He removed the cover plate screw, fitted the tab, and reinstalled the screw, with the transformer plugged in. The work was at the cover plate screw only, outside the receptacle. Any change to the receptacle itself, splitting it, rewiring it or adding a dedicated outlet, is 120 V branch-circuit work and goes to an electrician where local rules require one.

Labeled. A label on the transformer read that it powers the alarm panel and must not be unplugged or switched.

The conversation with the homeowner took a minute:

 TECH: The alarm's power plug was in the half of
       that outlet the wall switch controls. When
       the guests switched off at night, the panel
       ran on its battery until the battery gave out.
 CUSTOMER: So the new battery was not the problem?
 TECH: The old one really had failed, partly from
       this. The new one is fine. The plug is now
       on the half that is always on, screwed in,
       and labeled.

He confirmed the switch now operated only the lamp: switch off, the panel's AC indicator stayed on and a meter at the panel's AC input terminals still read the transformer's output voltage. Switch on, same.

Checking what the outages had cost

The new battery. It had been deep-discharged once already, less than a week into its life. He load-tested it: it passed comfortably. One deep discharge does far less harm to a healthy battery than repeated ones do to an old one. He noted the date of the discharge on the ticket.

The charge. He left the panel charging and checked the battery voltage before leaving, with the panel's own battery test showing normal.

The account. He confirmed the station received the AC restore under the test window, took the account off test, and confirmed with the operator that it was in normal service.

What the second visit added to the procedure

The repeat was not a lapse in skill on the first visit. The first tech answered the ticket he was given, which carried one event, and he answered it correctly. The fault in the process was that a low battery ticket arrived without the AC history that would explain it.

Two changes followed.

Low battery tickets now carry 30 days of signal history, and the dispatcher flags any AC loss in that window. A low battery with an AC loss before it is a power problem until proven otherwise; a low battery with no AC loss before it is a battery or charging problem. That one distinction would have closed this case on the first visit.

A battery replacement includes a look at where the transformer is plugged in. Is it on a switched outlet, a power strip, a timer, a ground-fault outlet that has tripped before, or a receptacle behind furniture where a vacuum cleaner gets plugged in? Each of those is common, and each turns a standby battery into a primary supply until it fails.

When the panel also carries fire devices

This panel was burglary only. Where a panel also monitors smoke or heat detectors, the power supply rules come from NFPA 72 in the edition as adopted. In substance, a commercial fire alarm system takes a dedicated branch circuit with its disconnect marked and secured, and even a household fire alarm system may not be fed from a switched outlet, with a plug-in transformer held in place by a restraining means. That is fire-side work, often separately licensed, and it routes through the fire-side procedure rather than through a battery call. See related: The Fire-Side Work and License Routing SOP.

References

• See related: How to Replace an Alarm Panel Battery and Load Test It
• See related: How to Size a Standby Battery for an Alarm Panel
• See related: How to Put an Alarm Account on Test and Take It Off
• See related: The Fire-Side Work and License Routing SOP
• NFPA 72, National Fire Alarm and Signaling Code, in the edition as adopted, for fire alarm power supplies